If you haven’t already noticed, this weekend is forecasted to be extremely cold. These steps can help you protect your plants from cold damage:
- Plant only varieties that are hardy for the area. Buy plants using the USDA hardiness zones.
- Given a choice, plant less-hardy plants in the highest part of the landscape. Cold air settles in the lowest area. During the winter, the coldest spots are often found on the north and northwest part of the property. The warmest spots are usually on the southern part of the property.
- Assess the property for microclimates. Changes in elevation, landform, soil properties, canopy cover, and proximity of structures determine a microclimate. Microclimates can be used to help protect plants by placing cold-sensitive plants near the part of the house that receives southern exposure or near larger plants or other structures.
- Protect plants from the cold wind with a fence or a tall evergreen hedge of trees or shrubs. They should be positioned anywhere cold winds can be an issue, most commonly on the northwest side of the planting.
- Radiational freezes occur on calm, clear nights when temperatures drop because of heat loss from the surfaces of objects. Canopies help reduce radiant heat loss from the plants and soil by preventing heat loss to the atmosphere. Plants growing closer to the ground are usually protected by heat radiating from the soil.
- Push container plants together can consider covering them to conserve heat. Wrap the bases of the containers in plastic, burlap, or blankets to reduce heat loss.
- Maintaining proper plant nutrition increases a plant’s tolerance to cold injury and acclimation to cold temperatures. Avoid the over-application of nitrogen in the fall, this causes flushes of new growth that is susceptible to cold temperatures. Soil sample to determine fertilization needs.
- A plastic covering provides excellent protection. Build a frame over the plant or plants, cover them with plastic, and secure the plastic to the ground with soil. Shade plastic to keep temperatures from building up inside. Plastic traps moisture and warm air as it radiates from the soil and blocks cold winds. Do not allow the plastic to touch plants.
- Mulching can reduce heat loss of the soil and retain moisture. Please maintain water requirements of ornamentals during the winter which is essential for a healthy and cold-hardy plant.
Cold damage may not be apparent in the plant for several days or weeks. To determine if your plants have been damaged by the cold, wait several days after a freeze and remove several buds, stems, and leaves (if present) from the plant. Use a sharp knife or razor blade to cut a cross-section of the bud’s top. If there is any discoloration in the bud, they have been damaged.
To determine if stems have been injured by the cold, peel the bark back to reveal the cambium layer (the layer directly under the bark). If there is any black or brown discoloration, the damage has occurred. Leaf damage may appear as obvious black or burnt foliage, usually occurring at the tip of the branches. Damage on buds, stems, and leaves may be localized and the entire plant may not be affected.
Waiting to prune after freezes have passed will guard against removing living wood. If localized damage has occurred to the foliage or stems, prune several inches below the injured tissue. Although injured buds may reduce or eliminate flowering or leaf emergence in the spring, no pruning is necessary.
If you have any questions about cold damage or protecting your ornamentals from the cold weather please contact your local county Extension agent.